A fire at Nebraska’s Fort Calhoun nuclear plant last June has dealt its owner a preliminary red finding from the Nuclear Regulatory Commission.On June 7, 2011, the reactor – shut down for refueling – had already declared an unusual event for flooding on the adjacent Missouri River when a fire in a switchgear room prompted operators to declare an alert, the next highest emergency category. According to the NRC, smoke and soot from the catastrophic failure of a feeder breaker disabled six of nine safety-related buses in the room and temporarily disabled spent fuel cooling. The Halon system, as well as plant and local volunteer firefighters, soon extinguished it.In its inspection report published Monday, the NRC noted the plant had replaced the breakers after problems reported to the agency in 2008. They were replaced with equipment from a different vendor in late 2009, and new cradles were installed to fit the exiting switchgear. Inspectors charge that the cradles were not installed correctly and the breakers were not properly cleaned in later maintenance. According to the report: “The preliminary (red) significance was based on the high fire frequency given the short period of time that the breaker cradles had been in service, the significant damage caused by a failure, and the inability of plant personnel to enter the switchgear rooms following a postulated fire in time to successfully minimize DC loads on the vital batteries.”The Omaha Public Power District acknowledged the finding, and on its website said it has already completed much of the work needed to address the agency’s concerns. On March 4 the utility began testing the equipment that replaced the breakers damaged in the fire.The NRC said it delayed the special inspection related to the event so as not to divert resources at the plant while it dealt with the flooding.
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